This invention relates to a device for the coupling of barlike structures and more particularly relates to an apparatus for splicing concrete reinforcement bars.
The splicing of bar-like structures and more particularly the splicing of reinforcement bars utilized in concrete construction has been accomplished in the past by a variety of means. One such means has been butt welding done on an individual basis by hand. This method has several disadvantages in that it is slow, expensive and the welding requires frequent quality inspection. Mechanical splices have also been utilized for the splicing of reinforcement bars. A typical mechanical splicing device is disclosed in U.S. Pat. No. 3,234,603 where a sleeve is placed around both ends of the bars to be joined and ancillary equipment is utilized to force molten metal into the sleeve thereby binding the bars together. A disadvantage of this mechanical splicing device is that it requires extensive ancillary equipment to be utilized to accomplish each splice.
A newer splicing device eliminating the need for ancillary equipment is a thermite-type coupler whose splice is based on a thermite-type-fueled exothermic reaction. Such thermite-type reaction usually occurs when a metallic oxide such as iron oxide or equivalent and a very active metal such as aluminum or equivalent are ignited forming, for example, a highly super-heated liquid iron and aluminum oxide slag. It should be noted that Thermit is listed as a trademark for metal compounds for welding, but your applicant's description of a thermite-type mixture is not limited to only the mixture as may be described under this trademark but includes any suitable material to produce a similar exothermic reaction. The coupling apparatus is comprised of an outer sleeve which is joined at its ends by collar members to an inner sleeve, the area defined between these sleeves being packed with a thermite-type mixture. The ends of two bars to be spliced are inserted into the inner sleeve and butted together. Fuse means extending through the outer sleeve into the thermite-type mixture holding area is used to ignite the thermite-type mixture. Ignition causes the reaction products to blow through one or several entry holes in the inner sleeve into the annulus between the reinforcement bars and the inner sleeve wherein the reaction products solidify around the bars thereby splicing the bars together along with the coupler.
There are many important factors to be considered when using a thermite-type coupler. First, the amount of the thermite-type mixture must be properly determined as too much thermite-type mixture will cause the inner sleeve to erode along the reinforcement bars as the thermite-type mixture blows out between the inner sleeve and the reinforcement bars. Alternatively, if too little thermite-type mixture is used, a splice of insufficient strength results. It has been found that air entrapped in the packing of the thermite-type mixture assists in the reaction as its acts as a propellant when heated to help force the thermite-type mixture into the clearance space between the reinforcement bars and the inner sleeve. A further factor to be considered when using a thermite-type coupler is the size of the entry hole since too large a hole allows for too violent a flow of thermite-type mixture while too small a hole can clog easily with solidified reaction products. An additional factor to be considered is the amount of clearance between the reinforcement bars and the inner sleeve. A tight clearance aids the splicing of the bars as it acts to resist the flow of the thermite-type mixture during the reaction thus keeping the reaction products around the reinforcement bars. Too great a clearance allows the reaction products to blow out the annulus. A means of stagnating the flow of the thermite-type mixture during the reaction is to increase the length of the inner sleeve to offer more flow resistance. It has also been found that texturing the inside of the inner sleeve allows for a more mechanical grip of the solidified reaction products on the reinforcement bars. Another major problem to contend with when using this type of coupling device is the considerable variance in the diameter of reinforcement bars to be joined. The annular space between the inner sleeve and the reinforcement bars must be small in order to prevent the reaction products from blowing out the ends of the annular space. This requirement of a close fit between the inner sleeve and the reinforcement bars becomes more acute when joining larger size reinforcement bars due to the considerable variations in the configurations and height of the ridges on the reinforcement bars.